1. Field of the Invention
The present invention relates to a radio-photoluminescence glass useful in dosimetry, hereinafter designated as "RPL dosimeter glass", of low energy dependence, and to a method of manufacturing same.
2. Description of the Prior Art
The dose indication of the RPL glasses possesses within the .gamma.-energy range between 40 keV and 60 keV a maximum of the energy dependence. This is rather disturbing when using the glass in dosimetry. Its suppression necessitates considerable additional expenditures for the encapsulation and mounting of such glasses, leading to a great increase in cost, an undesired increase in weight, and difficulties in cleaning the glasses. For this reason attempts have been made to reduce the quota of photo-electrons causing said maximum of the energy dependence by developing dosimeter glasses of a low mean nuclear charge number or atomic number.
Thus replacing barium metaphosphate Ba(PO.sub.3).sub.2 which has a high nuclear charge number by magnesium metaphosphate Mg(PO.sub.3).sub.2 is described in the journal "Nucleonics" vol. 18 (1960), pages 94 and 95. U.S. Pat. No. 3,554,920 discloses special glasses based on lithium metaphosphate LiPO.sub.3 and a lithium borate of the formula Li.sub.2 O. 4 B.sub.2 O.sub.3. However, the use of said special glasses in practice is prevented by their having too low a resistance to weathering.
Despite the small proportion of activating silver in the overall composition of RPL dosimeter glasses, this low silver content, because of its high nuclear charge number, decisively affects the energy dependence in basic glass compositions consisting otherwise of light chemical elements or compounds.
Thus it is known from "Health Physics" vol. 20 (1971), pages 662 and 663, to decrease the silver content of a dosimeter glass bearing the designation "Toshiba FD-3" while otherwise the basic glass composition in only slightly modified. Such a decrease in the amount of activator, however, results in a low sensitivity.
It is to be pointed out in particular that with the exception of the above-mentioned lithium borate glass of the formula Li.sub.2 O.4 B.sub.2 O.sub.3 the basic glass composition of all RPL glasses known at present is based on metaphosphates. Examples of such dosimeter glasses with metaphosphates as glass former are described, for instance, in German Application No. 1,596,750 published for opposition, German provisionally Published Application No. 1,621,004, and Austrian Pat. No. 257,858.
In such glasses the metaphosphate can partly be replaced by oxides, at least to a limited extent as this is described in the journal "Glastechnische Berichte" vol. 45, (1972), No. 6, pages 234 to 238. However, such a replacement results also in a reduction in sensitivity. Development of RPL glasses useful in dosimetry and being based on silica was also unsuccessful due to the low solubility of silver in silicates -- as follows from the "Journal of the Electrochemical Society" vol. 95 (1949), pages 70 to 79.
Silver-activated borate glasses have too low a weathering resistance and -- as compared with metaphosphate glass compositions -- too low a sensitivity.
Thus it appears not very promising further to develop RPL dosimeter glasses based on borate or silicate.
The aforesaid publications show that the efforts of those skilled in the art to produce RPL dosimeter glasses having a low energy dependence and at the same time further desirable properties such as high sensitivity, absence of fading at room temperature, and good resistance to weathering, up to now have not found any fully satisfactory solution, although such efforts have been continued extensively.